A simple slice model for prediction of macrosegregation in continuously cast billets

Abstract

Macrosegregation occurs in continuously cast products due to shrinkage, thermo-solutal natural and forced convection, floating of the solid grains and the deformation of the mushy zone, induced by the supporting rolls. A simple Lagrange-an traveling slice model has been successfully used in the past for prediction of the relations between the process parameters and the temperature field [1], grain structure [2], optimization of process parameters, and calculation of caster regulation coefficients. It is the purpose of this paper to demonstrate the applicability of this simple model for assessment of the macrosegregation. The main advantage of the slice model is its very fast calculation time in comparison with the complete 3D heat, solute and fluid flow model. The macroscopic model is based on continuum mixture theory by solving the enthalpy and concentration equations, while the microsegregation model is based on the Scheil rule. The fluid flow effects in the melt have been approximated by the increased solute diffusivity in the liquid phase of the slice. Ordinary, binary carbon steel is used for demonstration in this study. A sensitivity study of the approach on the recently introduced standard continuous casting configuration is performed with respect to inlet superheat, casting speed and cooling rates. The model surprisingly properly predicts the qualitative features of the macrosegregation pattern. Possible refinements of the model with respect to the additional physical mechanisms are discussed.